Aliens have been to Earth and it's not just the National Enquirer that says so.
A college professor is telling a story that sounds straight out of an internet conspiracy video.
He thinks aliens were here billions of years before humans.
The professor in question is Jason Wright and he works in the Astronomy and Astrophysics Department at Penn State University.
Wright believes artifacts of so-called "technological" species may exist in our solar system.
His paper, published in Cornell University's arXiv.org, says that we may soon discover "technosignatures" left behind by another species.
He suggests that this other tech-savvy species could have lived on a younger, wet Mars, a pre-greenhouse Venus or here on Earth.
It may be tough to prove because apparently most evidence would be long gone because of each planets change over time.
In other words, signs of alien life may have been erased on Earth because of stuff like erosion and plate tectonics.
However, Wright says proof may still be found under the surfaces of Mars and the Moon.
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